Conformal coating of polymer fibers on nonwoven substrates

Abstract

The present invention describes a novel process for the conformal coating of polymer fibers of nonwoven substrates. This process is based on modification of polymer fiber surfaces by controlling the degree of etching and oxidation to improve adhesion of initiators to the surface and to facilitate subsequent conformal polymer grafting. The modified fiber surfaces render new functionalities to the surface, such as increased hydrophilicity, attached ligands or changed surface energy. The invention includes the modified polymer fibers produced by the process described herein.

What is claimed is: 
     
       1. A process to modify a fiber surface of a polymer nonwoven substrate to obtain a conformal coating, comprising:
 1) increasing roughness of a fiber surface and increasing the hydroxyl, carbonyl and any other oxygen containing group through exposure to UV in air at a wavelength between 150-300 nm, wherein said exposure to UV in air generates ozone; 
 2) soaking the substrate with a solution containing both a monomer and an initiator; 
 3) sandwiching the soaked substrate obtained from step 2 between two glasses; 
 4) exposing the substrate to UV or heat for grafting to form the conformal coating; and 
 5) washing and drying the substrate. 
 
     
     
       2. A process as defined in  claim 1 , wherein the polymer nonwoven substrate is polyolefin fiber, aramid fiber, cellulose fiber, polyamide fiber, polyester fiber, polyvinyl alcohol fiber, polyethylene naphthalate fiber, polyacrylonitrile fiber, polyurethane fiber, liquid crystal copolyester fiber, rigid rod fiber, or a combination thereof. 
     
     
       3. A process as defined in  claim 1 , wherein the polymer nonwoven substrate is a flat sheet, a roll or a stack. 
     
     
       4. A process as defined in  claim 1 , wherein the polymer nonwoven substrate is a staple or continuous fiber. 
     
     
       5. A process as defined in  claim 4 , wherein the polymer nonwoven substrate has round, triangle, square, or any irregular shapes of cross-sections. 
     
     
       6. A process as defined in  claim 1 , wherein said monomer is a bifunctional molecule which can polymerize via radical polymerization and provide functional groups chosen from hydroxyl, amine, carboxylic acid, aldehyde, formamide, pyridine, pyrrolidone, and epoxy. 
     
     
       7. A process as defined in  claim 1 , wherein said solution comprises a solvent selected from an alcohol or hydrocarbon which dissolves at least 0.5% of the monomer. 
     
     
       8. A process as defined in  claim 1 , wherein said initiator is a photosensitizer. 
     
     
       9. A process as defined in  claim 8 , wherein said photosensitizer is benzophenone, anthraquinone, or naphthoquinone. 
     
     
       10. A process as defined in  claim 1 , wherein said solution contains 0.5% to 20% by weight of monomer. 
     
     
       11. A process as defined in  claim 1 , wherein unreacted monomers or unattached homopolymers are removed by water, alcohol or hydrocarbon. 
     
     
       12. A process as defined in  claim 1 , wherein the polymer nonwoven substrate has a uniform or gradient distribution of a second polymer inside the nonwoven substrate. 
     
     
       13. A process as defined in  claim 1 , wherein the polymer nonwoven substrate is polypropylene (PP) fiber or polybutylene terephthalate (PBT) fiber. 
     
     
       14. A process to modify a fiber surface of a polymer nonwoven substrate to obtain a conformal coating, comprising:
 1) increasing roughness of a fiber surface and increasing the hydroxyl, carbonyl and any other oxygen containing group through exposure to UV in air at a wavelength between 150-300 nm, wherein said exposure to UV in air generates ozone; 
 2) soaking the substrate with a solution containing both a monomer and an initiator; 
 3) sandwiching the soaked substrate obtained from step 2 between two glasses, wherein said sandwiching promotes, during subsequent grafting, formation of a saturated vapor phase near the surface of the substrate; 
 4) exposing the substrate to UV or heat for grafting to form the conformal coating; and 
 5) washing and drying the substrate.